Abstract: A power interface circuit for normally deenergized loads includes the capability to test the operation and connections thereof without any possibility of accidental activation of the load. Three input signals may be received by the power interface circuit which supplies power to a load if two out of three of the input signals indicates activation of the load. A normally closed switch which ordinarily provides power directly to the voter is opened during testing so that the voter is supplied with a reduced power that is insufficient to activate the load. The normally closed switch is closed if any of the input signals indicate activation of the load. Current sensors are included in the power interface circuit to detect all possible logic combinations for activating the load and to detect the operation of the normally closed switch.

Abstract: A deep beam head for a nuclear reactor and an improved reactor containing such a head where the upper horizontal support plate of a calandria in the reactor forms a sealing plate for the reactor vessel. The sealing plate has a ring member about the upper periphery thereof that is secured to the top of the pressure vessel cylindrical wall and reinforcing members extend across the sealing plate and are welded to the ring, while transverse cross-members extend across the sealing plate and are welded to the reinforcing members. The calandria may be removed from the reactor while attached to the ring member to provide ready access to the reactor internals.